In the related art, an HFC refrigerant used for a centrifugal chiller has a Global Warming Potential (GWP) value in the hundreds to thousands, and thus, it is necessary to switch from the HFO refrigerant having a GWP value in the hundreds to thousands of GWP to an HFO refrigerant having a GWP value of one digit in consideration of an environment. In order to cope with this, a low pressure refrigerant such as HFO-1233zd (E) without combustibility may be used as a refrigerant for a chiller.
In general, the centrifugal chiller has an oil tank in which a lubricant supplied to the turbo compressor is stored. The oil tank is equalized to a low pressure side (evaporator side) of the centrifugal chiller, and thus, in a case where a low pressure refrigerant is used, if a pressure in the oil tank is equal to or less than the atmospheric pressure, a gas volume increases. That is, compared to a chiller which uses a high pressure refrigerant, in a chiller which uses a low pressure refrigerant, in a case where a pressure of the refrigerant having the same mass dissolved into the lubricant in the oil tank decreases and the refrigerant evaporates, a volume of the evaporated refrigerant increases, and foaming easily occurs in the lubricant in the oil tank. Particularly, at the time of start-up where a pressure reduction speed on a low pressure side is large, foaming easily occurs in the lubricant in the oil tank.
PTL 1 discloses that when a turbo compressor starts-up, after the start-up is performed at an opening degree at which an opening degree of a suction capacity controller is smaller than a target opening degree, the opening degree rapidly increases to the target opening degree such that an operation time in which the opening degree is less than the target opening degree can be set as short as possible to reduce a passage resistance of the refrigerant, and a decrease in a pressure on a downstream side of the suction capacity controller is suppressed so as to suppress the occurrence of foaming.